Germination is involved in the production of malt from cereal grains. In cereals such as barley, root (chit) emergence indicates that germination has taken place. However, in the malting process the term “germination” is used to describe the long growth/modification phase between steeping and kilning. The embryo is the germinating organ of the grain. It is composed of the axis and the scutellum. The scutellum is the single (mono) cotyledon of the grain and is a food storage organ. For example, it stores lipids, proteins, and vitamin B like the aleurone layer. The axis contains the shoot and the roots. The shoot is covered by the colepotile. Both tissues constitute the acrospire. The tiny roots are covered by the coleorhizae. Both tissues constitute the chit. Hydration (wetting/steeping) of the embryo at normal temperatures in the presence of air increases its metabolism. Increased metabolism causes the chit and the acrospire to elongate. The acrospire grows slowly along the top of the grain under the pericarp covering layer and exits at the nonembryo end of the grain if the grain is overmalted. The length of the acrospire is used as a modification test. The chit elongates rapidly and ruptures the covering layers before extensive elongation of the acrospires has occurred. This early rupturing of the covering layer by the chit is called germination. During the germination process the axis of the embryo produces gibberellic acid (GA3). In general, emergence of the chit indicates that gibberellic acid has been transported from the axis to the aleurone layer and that endosperm degrading enzymes are being produced.
Dormant grains do not germinate and will not make acceptable malt. Dormancy can be genetic and can be induced by unfavorable climatic (cold) conditions. Dormancy can be broken by warm storage of dried (e.g., 11% moisture) barley. Uneven germination will produce unevenly modified malts. During malting, germinated grains will absorb added gibberellic acid faster than ungerminated (dormant) grains, causing even greater unevenness of modification. Uneven modification is a primary factor in poor brewhouse performance. Absorbed gibberellic acid complements the natural levels of gibberellic acid produced by the embryo. Optimal levels of gibberellic acid will produce optimal levels of endosperm-degrading enzymes. However, some barley varieties do not require additional levels of gibberellic acid to malt well.
Respiration (oxygen uptake and loss of carbon dioxide) promotes germination and enzyme production in malting grains. High respiration and excessive root and shoot growth cause high malting loss. Malting loss reflects potential loss of starches available for mashing. In the past, malting loss was reduced in some quarters by applying potassium bromate. Today, malting loss is controlled by humidity, temperature, and appropriate growth time during the malting process.
Barleys that germinate on the ear in the field or in storage before steeping are described as having pregerminated. Pregerminating potential may be genetic and/or climatic. Pregermination of cereals such as barley and wheat can destroy the processing potential of the grain, encourage microbial growth, and initiate premature enzyme development, which damages the malting potential of barley and the baking potential of wheat.
Germination energy, germination capacity, embryo viability, water sensitivity (vigor in steeping), and the pregermination levels of cereals can be detected using recommended tests.